A basic grant provides the means to study the impact on arboviral transmission cycles of ecological changes in a tropical forest caused by formation of a 300 km squared hydroelectric lake in the Bayano river of Panama. The study site is located on a ridge that has become an island in the lake. This is a request for supplementation of the basic grant to permit extension of the studies from the single site on an island to several additional sites on the shore. In addition, surveillance of the human population for arbovirus disease or infection will provide information on the effect of these cycles on the human population. The large areas of data which have been accumulated must now be subjected to biostatistical analysis and interpretation.